Memoirs of Dr. Joseph Priestley

by Joseph Priestley

From this brief account of the first stage of Dr. Priestley’s chemical labours, it appears that during the short period of two years, he announced to the world more facts of real importance, and extensive application, and more enlarged and extensive views of the œconomy of nature, than all his predecessors in pneumatic Chemistry had made known before.

In 1776 his observations on respiration were read before the Royal Society; in which he clearly discovered that the common air inspired, was diminished in quantity, and deteriorated in quality, by the action of the blood on it through the blood vessels of the lungs; and that the florid red colour of arterial blood, was communicated by the contact of air through the containing vessels. His experiments on the change of colour in blood confined in a bladder, took away all doubt of the probability of this mode of action. I cannot help thinking that the circumstance of Dr. Priestley’s mind being so much occupied with the prevailing theory of Phlogiston, was the reason why he did not observe that the diminution of the air, and the florid colour of the arterial blood was owing to the absorption of the pure part of the atmosphere, rather than to any thing emitted from the blood itself. This part of the theory of respiration Mr. Lavoisier has certainly established; though it is by no means ascertained as yet whether the vital part of the atmosphere inspired, is wholly and alone absorbed, or whether in reality something is not contributed in the lungs to the formation of the fixed air found after expiration.[53]

[53] That azote is absorbed during respiration as Dr. Priestley supposed contrary to Mr. Lavoisier’s opinion, is made extremely probable by the experiments of Mr. Davy, whose accuracy is well known. Researches, p. 434. The formation of water in this process, is certainly no more than conjecture as yet. Dr. Bostock has lately published a very useful and laborious history of discoveries relating to respiration, both anatomical and pneumatical.

In 1778 Dr. Priestley pursued his experiments on the property of vegetables growing in the light to correct impure air, and the use of vegetation in this part of the œconomy of nature. A discovery which was announced to several men of science in England previous to the publication of the same ideas by Dr. Ingenhouz.[54] Indeed from its having been communicated to M. Magellan whose pleasure and whose occupation it was, to give information of new facts to his philosophical correspondents, and of this in particular to Dr. Ingenhouz then engaged in similar researches, there is hardly a doubt but the latter knew of the experiments then pending on the subject by Dr. Priestley.

[54] Doctrine of Phlogiston established, p. 107, et. seq. The theory of the amelioration of impure air by the absorption and excretion of vegetables growing in the light, has been doubted by Dr. Darwin in his Phytologia, and opposed by Count Rumford in a paper published in the transactions of the Royal Society, for 1787: also by Dr. Woodhouse of Philadelphia, Nicholson’s Journal, for July 1802, and by Mr. Robert Harrup, Nicholson’s Journal, for July 1803.

It is painful to notice these aberrations from propriety in the conduct of men highly respectable in the philosophical world, arising from an over anxious avarice of literary fame, and an improper jealousy of the reputation of another. Not that it derogates from the character of a philosopher to wish for the applause of those who know how to appreciate his merit, or who are benefited by his exertions; such an anxiety is laudable when it does not lead to encroachments on the literary rights of others; nor is it at all desireable under the present circumstances of human nature, to expect from men of science an attention to their pursuits arising from motives of pure benevolence alone, and excluding all views, hopes, and expectations of the gratifying tribute of public approbation. I believe no man ever laboured with a more single eye to public utility than Dr. Priestley. But consideration in society, and the respectability attendant upon great talents, and great industry, successfully employed for the benefit of mankind, is a motive to useful exertion so universal, so honest, so laudable, and withal so powerful, that it is the common interest, as well as the duty of society, to bestow it liberally where it has been earned faithfully, and to concede it to those only, who have really deserved this honourable reward.

From this period Dr. Priestley seems to have attended to his pneumatic experiments as an occupation; devoting to them a regular portion of his time. To this attention, among a prodigious variety of facts tending to shew the various substances from which the gasses may be procured; the methods of producing them; their influence on each other, and their probable composition, we owe the discovery of vitriolic acid air, of fluor acid air, of vegetable acid air, of alkaline air, and of dephlogisticated nitrous air, or gazeous oxide of azote as it has been called, the subject of so many curious experiments by Mr. Davy. To these we may add the production of the various kinds of inflammable air by numerous processes that had escaped the observation of Mr. Cavendish; in particular the formation of it by the electric spark taken in oils, in spirits of wine and in alkaline air; the method of procuring it by passing steam through hot iron filings, and the phenomena of that hitherto undetermined substance the finery cinder, and its alliance to steel. To Dr. Priestley we owe the very fine experiment of reviving metallic calces in inflammable air and its absorption in toto, apparently at least, undecomposed. He first ascertained the necessity of water to the formation of the gasses, and the endless production of air from water itself.

Dr. Priestley’s experiments on this subject, to wit: the generation of air from water, opened a new field for reflection, and deserves more minute notice. No theory has yet been proposed adequate to the explanation of the facts. He had before remarked that water was necessary to the generation of every species of air, but the unceasing product of air from water had never been before observed.

In his first set of experiments he procured air, by converting the whole of a quantity of water into steam: then, to obviate the objection to the water having imbibed air from the atmosphere he put the water on mercury in long glass tubes immersed in mercury: in a third process he used no heat, but merely took off the pressure of the atmosphere. In all these cases a bubble of air was extricated from the water, which being separated by inclining the tube, another bubble was again produced on each repetition of the experiment. That this could not be air imbibed from the atmosphere appeared from this, that though the first portions were generally purer than atmospheric air, the next became less pure, and at length wholly phlogisticated.

It did not appear that the addition of acids, enabled the water to yield more air, nor did he succeed in attempting to convert the whole of a given quantity of water into air, although exposing the water confined over mercury to heat, and separating the air produced, it still continued to produce more air for twenty or thirty repetitions of the experiments. When a certain proportion of air was thus produced at any one time, no continuance of the experiment would encrease the quantity until it was separated. Hence he concludes that the longest continuance of water in the state of vapour would not convert it into air. The water used was pure distilled water previously boiled to separate any adventitious air that might have been imbibed from the atmosphere. The precautions he used, and the replies to such objections as he foresaw the experiment would be liable to, are detailed in the papers he published on the subject, to wit, a separate pamphlet published in England in 1793, and a communication in the Am. Ph. trans, v. IV. p. 11-20.